Speaking at today’s event, Garda Assistant Commissioner Michael Finn said that the new testing was being introduced to drug driving becoming a real problem on Irish roads.

He said that cannabis was the drug of choice for offenders, who tended to be young men.

Of the 3,000 specimens Garda tested last year, 24 per cent were positive for drugs other than alcohol.

After cannabis, benzodiazepines were the main drug detected in drivers.

The new tests mean Garda will not have to prove a motorist is impaired when it comes to certain level of cannabis, cocaine and heroin before they charge them with a road offence.

Despite the limits, drivers are being warned to not “take drugs and drive”.

The Medical Bureau of Road Safety says that unlike alcohol, drug measures are not regulated so even a single joint could put motorists over the new limits.

“Don’t drink and drive, don’t take drugs and drive,” is the RSA’s message.

Its Chief Executive Moyagh Murdock said that persons driving under the influence of drugs are a danger to themselves and others.

She said: “Our own research shows that many drug drivers incorrectly believe that certain drugs make them better drivers and imagine themselves at low risk of collision.

“They also tend to overestimate their driving ability and show little understanding of how drugs affect their driving. Many have poor awareness of the impairing effects of drugs and make bad decisions about driving as a result.”

For those who test positive for prescription or over-the-counter medicines, Garda say that as long as these medicines are taken in accordance with healthcare advice and do not impair driving, motorists “have nothing to be concerned about.”